The invention relates to a process for the production of chlorine-free cyclopropanecarboxylic acid esters of Formula 1 by reacting gamma-butyrolactone with hydrogen chloride and a butyl alcohol to form a gamma-chlorobutyric acid ester 2 and subsequent cyclization with an alcoholate to 1, well as interesterification of 1 to a higher-boiling ester 3. ##STR1##
Syntheses of gamma-chlorobutyric acid esters and cyclopropanecarboxylic acid ester, starting with the readily accessible gammaa-butyrolactone, have been known from the literature.
In his article, Reppe described (Reppe, Annalen der Chemie 596: 163-224[1955]) the synthesis of gamma-chlorobutyric acid methyl, ethyl, propyl and butyl esters as a single-step process of introducing hydrogen chloride into a solution of gamma-butyrolactone and the corresponding alcohol, using zinc chloride as the catalyst. Due to the formation of high-boiling compounds, by a secondary reaction, Reppe achieved only low yields, for example, 50.4% in case of the methyl ester.
Therefore, a process to produce cyclopropanecarboxylic acid esters has been suggested in DOS No. 2,751,134, operating at low temperatures of 0.degree.-20.degree. C. and with thionyl chloride in place of hydrogen chloride. The yield of methyl ester, 91.3%, is relatively high. However, this process has 2 drawbacks: the high price thionyl chloride and the formation of gaseous sulfur dioxide during the reaction. This latter gas must be destroyed or removed by expensive technical measures for reasons of environmental protection.
Several of strong alkaline compounds have been proposed for the cyclization of gamma-chlorobutyric acid ester; for example, sodium amide (U.S. Pat. No. 3,294,833), sodium methylate in toluene DOS No. 1,939,759 and DOS No. 2,751,133), sodium tert amylate (M. and S. Julia et al., Bull. Soc. Chim. Fr. 1960 No. 2: 304-312) and sodium methylate in methanol (German Pat. No. 2,941,211).
The last-mentioned patent, wherein additional literature references are cited and discussed, contains the statement that industrially interesting yields can only be obtained by using, as the condensation agent, sodium hydride, sodium amide or alcohol-free alcoholates. The presence of alcohols leads to secondary reactions. In the cyclization of gamma-chlorobutyric acid ethyl ester with sodium methylate in ethanol, the 4-ethoxy-butyric acid ethyl ester is formed as a by-product by substitution. The analogous problem is said to occur when using the reseective methyl compounds.
The process of German Pat. No. 2,941,211 solves the problem of yield when employing the methyl and ethyl esters, by applying high temperatures--in a temperature range of 90.degree.-200.degree. C.--and by the utilization of superatmospheric pressure.
This temperature range, in the system of gamma-chlorobutyric acid ethyl ester, sodium amylate in tertamyl alcohol, leads, as demonstrated by Julia et al. (see above), to yields of only 45% of theory. Accordingly, a clear teaching can be gleaned from the totality of the literature citations that the presence of alcohols represents a disturbing factor in cyclization--except for the use of the systems of sodium ethylate in ethanol and sodium methylate in methanol at tempeatures at 90.degree.-200.degree. C.
However, these two systems have the disadvantage that expensive pressurized devices are required, and that, after reaction and addition of water, an aqueous phase containing sodium chloride, alcohol and reaction products is obtained which must be worked up by means of repeated extraction.
Furthermore, a grave drawback of the process in German Pat. No. 2,941,211 is the insufficient purity of the thus-obtained cyclopropanecarboxylic acid esters, the chlorine content of these esters being generally 100 to 1,000 ppm or higher. Due to these high chlorine contents, these esters cannot be catalytically hydrogenated to obtain cyclopropylcarbinol.
In addition, the reactors would be subject to corrosion, and the hydrogenation catalyst would be poisoned. The chlorine content of the esters intended for catalytic hydrogenations must be below 10 ppm.
Therefore, only expensive reagents, such as lithium aluminum hydride, are suitable for the reduction of the chlorine-containing cyclopropanecarboxylic acid esters.
Also, all of the conventional methods require expensive chemicals, pressurized apparatus, and lead to problems with waste disposal. Thus, a process is desired wherein gamma-butyrolactone would be converted in a single-step process into a gamma-chlorobutyric acid ester by reaction with hydrogen chloride and an alcohol, and this product could be cyclized without excess pressure. It would be also desirable for the chlorine content of the product to be sufficiently low that the thus-formed cyclopropanecarboxylic acid ester could be hydrogenated catalytically, for example, to obtain cyclopropylmethanol.